My Mythical Convergence Box was working ok as a mythtv backend but as a server it was frustratingly slow: slow to boot firefox, task switch, run wow, whatever. I was itching to upgrade it.
I decided the cheapest solution was a good old processor/motherboard/memory upgrade so now the box has a Dual Core 64 bit AMD processor, a AMD690GM motherboard and 2g of 800Mhz ram. I also splurged on a 750G SATA hard disk since they were on special offer. I installed the native Ubuntu 64 bit version for a free 64 bit state of the art operating system. Why pay more?
This fixed the performance problems 
Myth and everything all worked fine, 64 bits did not cause any compatability problems. The 750G disk will hold about 375 hours of TV recordings, should I have 15 solid days (and nights) spare to watch tv.
The motherboard I bought had an AMD/ATI chipset so my biggest problems were getting WoW to run without crashing, ATI's linux drivers not being the best. I used the ones installed by ubuntu, I tried installing newer ones at one point but they made no difference. I tweeked more things than I can remember googling for but the most important thing is to add
SET gxAPI "opengl"
to WTF/Config.wtf as otherwise it tries to runs in direct 3d mode and immediately dies with a fatal exception. The frame rate was then crap and I had to turn all the settings down but it does run wow acceptably: while setting it up I became preoccupied with gathering turtle meat.
The graphics are still odd, there is something wrong with the colour balance that makes everything looks cartoonish and when watching recordings the top line on the display flickers. It's awfully tempting to get an nvidia card..
On my desktop Wow still runs just fine, even with mythtv showing Alien vs Predator on the second monitor. Add a nice mug of coffee and life is sweet.
Peter's Moblog
I had some interesting fun with WoW a while back under Linux. I only had two gig of memory, and after a raid or two, it became very sluggish under windows and it ended up thrashing the hard drive, WoW usually ends up using 1.2gig of memory or so. Using stock standard Wine under Ubuntu 7.1, WoW actually ran faster and smoother than when in Windows. I put this down to better memory usage and better disk caching. I couldn't stick with it though :( our guild uses Vent, and although i could get Vent working on its own, and WoW working on it's own, they refused to work together properly (and the in game voice system is a joke ).
I went and got 4gig of memory(up from 2), although Vista(32bit!) won't detect all 4, it will detect 3, which i found still gives a huge performance boost in most games, and it no longer thrashes the drive.